Based on the comic book series by Robert Kirkman, this gritty drama portrays life in the weeks and months following a zombie apocalypse.

Led by police officer Rick Grimes, his family and a group of other survivors find themselves constantly on the move in search of a safe and secure home.

But the pressure each day to stay alive sends many in the group to the deepest depths of human cruelty, and Rick discovers that the overwhelming fear of the survivors can be more deadly than the zombies walking among them.

The show is now in its eighth season. The first episode Mercy was shown last night.

The Walking Dead TV series. Police officer Rick Grimes leads a group of survivors in a world overrun by zombies

Here's what three review sites had to say:

Forbes: "All told, this season premiere was much less gruesome and hard to watch than Season 7's, but also a lot less interesting.

"All out war has begun, but for all their firepower, Rick and his group just couldn't get it right.

"It's not that hard to just shoot Negan, but this show makes it seem that way.

"I've been very hopeful that The Walking Dead would redeem itself tonight after a long slog of a season last year. It wasn't as bad as all that, but it didn't live up to all the hype either.

"Maybe it's all a sign of fatigue. It's tough to keep going and keep things interesting for eight seasons.

"What we loved about the earlier seasons - a smaller group on the move, scavenging and surviving - has simply changed into something else.

"It's like an entirely different show now, and for some that may be just what they want. For me, I keep pining for what's been lost, and tonight's nods to the pilot only made that worse."

IGN: "The most staggering thing about Mercy, despite all the bullets whizzing and cars exploding, was how dry it was overall.

"I'll always give The Walking Dead points for the moments when it tries to elevate itself over run-of-the-mill horror fare, and it's given us some truly mesmerizing moments over the years, but this assault on the Sanctuary, in an attempt to take out Negan and his group of marauders from all angles, wound up feeling a touch toothless.

"Sometimes the show just needs violence to be violence and not an artistically cut-up piece of meandering meditation, overly steeped in the gravity and sentiment of the moment."

Den of Geek: "The structure of the episode is interesting to watch, and it's a nice contrast between reality and fantasy, but after eight seasons, Rick's inspirational speeches are starting to fall a little flat.

"We've heard it all before, and Scott M. Gimple isn't able to reinvent the wheel as far as he's concerned.

"Ezekiel and Maggie's speeches work a little bit better, if only because Ezekiel gets to quote Shakespeare and Maggie gets to talk about the planning aspects of their fight and how much work they'll have to do in the coming days.

"It's an interesting dichotomy in leadership styles, but it doesn't work as well as Maggie's quiet little joke about being able to wage war until the second trimester, or the little scenes of Carol and Tara hanging out and waiting for the zombie parade to approach their overpass."